Prostate Cancer (PCa) is the most common solid tumor among American men and the second leading cause of cancer death. Surgery, radiation and active surveillance (AS) may all be appropriate treatments for men newly diagnosed with localized PCa. The 2008 AHRQ comparative effectiveness report on therapies for localized PCa determined that no one therapy can be considered the preferred treatment due to the limitations in the body of evidence as well as the likely tradeoffs an individual patient must make between estimated treatment effectiveness, necessity and adverse effects. Simply put, there is a pressing need for additional and better studies on the comparative effectiveness of treatments for localized PCa. In 2010, AHRQ funded the Comparative Effectiveness Analysis of Surgery And Radiation for localized PCa (CEASAR) study. CEASAR consists of a prospective, population-based cohort of 3691 men diagnosed with localized PCa in 2011 who were treated with contemporary therapies, including AS. CEASAR collected baseline patient-reported health-related quality of life, clinical, and sociodemographic data. We then obtained clinical and patient reported outcomes at 6 and 12 months after enrollment. We also performed medical record review at 1 year, collecting clinical information and data on the technical details of the interventions, complications, short-term cancer recurrence rates, and quality-of-care indicators. We will leverage the existing CEASAR study and collect 3- and 5-year follow-up data to: (1) Compare the effectiveness and harms of contemporary surgery, radiation and AS in terms of 3- and 5-year patient-reported outcomes and cancer control. We will identify and analyze outcome profiles associated with each therapy that can be used to inform patient specific outcome trajectories when selecting therapy and after treatment. (2) Identify patient-level characteristics that influence the comparative effectiveness and harms of treatment. We will assess the influence of race, co-morbid conditions and socio-economic status on 3- and 5- year patient-reported outcomes in the entire group and in individual treatment groups to identify subgroups of patients who respond uniquely to certain treatments. (3) To evaluate the association of quality of care with clinical and patient-reported outcomes. We will assess the relationship between pre-specified quality indicators and 3- and 5-year outcomes in CEASAR. We will then re-assess the comparative effectiveness of the various treatments, controlling for quality measures found to independently influence outcomes. By understanding what works, in which patients and in whose hands in localized prostate cancer, we will be advancing AHRQ's mission of improving the quality, safety and effectiveness of healthcare in this common condition.